Google released in the US a new version of Google Talk designed specifically for the iPhone and iPod Touch browsers. Here is more info:

In addition to sending your friends Gmail messages from your iPhone, you can now chat with them while you're on the move, too! In your iPhone browser, just go to www.google.com/talk, sign in and start chatting. That's it. Google Talk runs entirely in the browser so there's no need to download or install anything.

There are some differences from using Google Talk on your computer. For instance, in order to receive instant messages with Google Talk on your iPhone, the application needs to be open in your Safari browser. When you navigate away to another browser window or application, your status will be changed to "unavailable" and your Google Talk session will be restarted when you return.

Features:-Chat with your Google Talk contacts in real time. Send and receive instant messages in chat sessions with your contacts. Move easily between multiple open chats.-View and search for your Google Talk contacts. See the availability and status message of your contacts and change your own status on the go.-Go off the record if you don't want to store your chats. Off the record chats are not stored on Gmail.